1. Field of the Invention
The present invention relates to an apparatus of fabricating a semiconductor device, and more particularly, to a substrate supporting means for a plasma apparatus of fabricating a liquid crystal display device.
2. Discussion of the Related Art
Flat panel display (FPD) devices having portability and low power consumption have been a subject of increasing research in the present information age. Among the various types of FPD devices, liquid crystal display (LCD) devices are commonly used in notebook and desktop computers because of their high resolution, capability of displaying colored images, and high quality image display.
In general, an LCD device is a non-emissive device having an array substrate, a color filter substrate and a liquid crystal layer interposed between the array substrate and the color filter substrates, and displaying images by making use of optical anisotropy properties of the liquid crystal layer. In addition, an LCD device is fabricated by repeating a deposition step of a thin film on a substrate, a photolithographic step using a photoresist, a selective etching step of the thin film and a cleaning step of the substrate. These steps for a fabrication process of an LCD device may be performed using an apparatus having a process chamber under an optimum condition. A plasma apparatus where source gases are excited to radicals of a plasma state by a high frequency power is used for deposition, etching and cleaning steps of an LCD device. Recently, a plasma enhanced chemical vapor deposition (PECVD) apparatus has been widely used as a plasma apparatus.
FIG. 1 is a schematic cross-sectional view showing a plasma apparatus for a liquid crystal display device according to the related art. In FIG. 1, a plasma apparatus includes a process chamber 100 having a lid 112 and a chamber body 114. A gas inlet pipe 122 is formed through a middle portion of the lid 112 and a backing plate (not shown) under the lid 112. A shower head 120 having a plurality of through holes (not shown) is formed under the backing plate. Accordingly, source gases are injected to the shower head 120 through the gas inlet pipe 122 and are dispersed into a space over a susceptor 130 in the process chamber 100 through the plurality of through holes. Since a gas dispersion unit including the backing plate and the shower head 120 is connected to a high frequency (e.g., a radio frequency) power supply unit 124, the source gases are excited to have a plasma state. For example, the shower head 120 of the gas dispersion unit may function as an upper electrode to obtain a plasma state of the source gases. In addition, the chamber body 114 has a slot valve 146 for transferring a substrate “S.”
The susceptor 130 is disposed in the chamber body 114. After a substrate “S” is transferred into the process chamber 100, the substrate “S” is placed on the susceptor 130. A heater (not shown) for heating the substrate “S” during a fabrication process is formed in the susceptor 130 and is connected to an external power source (not shown). For example, the susceptor 130 may function as a lower electrode to obtain a plasma state of the source gases. A susceptor-supporter 134 extends from a rear central portion of the susceptor 130 and a susceptor driving unit 144 such as a motor is connected to the susceptor-supporter 134 to move up and down the susceptor 130. In addition, a gas outlet pipe 142 is formed through a bottom portion of the chamber body 114. The gas outlet pipe 142 is connected to a vacuum pump (not shown) to evacuate residual gases and particles in the process chamber 100 after the fabrication process.
A plurality of lift pins 150 are formed to penetrate the susceptor 130 perpendicularly. The substrate “S” is supported by the plurality of lift pins 150 while the substrate “S” is transferred from a robot arm (not shown) to the susceptor 130 before the fabrication process and from the susceptor 130 to the robot arm after the fabrication process. Accordingly, the susceptor 130 moves up and down by the susceptor driving unit 144 while the substrate “S” is transferred into and out of the process chamber 100, and the plurality of lift pins 150 are protruded above and indented under a top surface of the susceptor 130. As a result, the substrate “S” is transferred from the plurality of lift pins 150 to the susceptor 130, and vice versa.
FIGS. 2A to 2C are schematic cross-sectional views showing a transfer process of a substrate in a plasma apparatus for a liquid crystal display device according to the related art. In FIG. 2A, a substrate “S” on a robot arm 160 is transferred into a process chamber 100 (of FIG. 1) and placed over a susceptor 130. A plurality of lift pins 150 is protruded above a top surface of the susceptor 130 through a plurality of lift pin holes 136, and a bottom surface of the substrate “S” is separated from the plurality of lift pin 150. Next, the substrate “S” contacts the plurality of lift pins 150 by moving down the robot arm 160.
In FIG. 2B, the robot arm 160 is returned to an exterior of the process chamber 100 (of FIG. 1) and the substrate “S” is supported by the plurality of lift pins 150 protruded above the top surface of the susceptor 130.
In FIG. 2C, since the susceptor 130 moves up by a susceptor driving unit 144 (of FIG. 1), the plurality of lift pins 150 relatively move down through a plurality of lift pin holes 136. Accordingly, the substrate “S” is placed on the top surface of the susceptor 130. The lift pin 150 has a greater diameter at an upper portion 150a than at the other portion to prevent complete separation of the lift pin 150 from the lift pin hole 136 of the susceptor 130. Similarly, the lift pin hole 136 also has a greater diameter at an upper portion 136a than at the other portion.
Even though not shown, the susceptor 130 having the substrate “S” thereon moves up to a reaction region of the process chamber 100 (of FIG. 1), and a thin film is formed on the substrate “S” due to source gases, a high frequency power and a heat. After the thin film is formed, the substrate “S” is supported by the plurality of lift pins 150 by moving down the susceptor 130. Next, the robot arm 160 is placed between the substrate “S” and the plurality of lift pins 150 and then the substrate “S” is transferred out of the process chamber 100 (of FIG. 1).
Since the plurality of lift pins are formed through the susceptor having a heater therein, the plurality of lift pins may be defected by a heat of the heater during a fabrication process. Specifically, lift pins adjacent to the heater may be easily broken due to a high temperature. Moreover, when the substrate is placed on the plurality of lift pins, the substrate may be defected by sliding over from a predetermined position. Recently, as a size of the substrate increases, more numbers of lift pins are required to support the substrate. When lift pins penetrating a central portion of the susceptor are defected, a corresponding central portion of the substrate is not supported, thereby the substrate warped or broken.
In addition, since the susceptor has a plurality of lift pin holes corresponding to the plurality of lift pins, a heat from the heater in the susceptor is released through the plurality of lift pin holes and is not completely transmitted to the substrate. Accordingly, an optimum fabrication process of a thin film is not obtained. Further, since a plasma density at a portion adjacent to the plurality of lift pin holes is different from that of the other portions, the thin film on the substrate have a non-uniform thickness. This non-uniform thickness of the thin film may deteriorate a resultant LCD device.